If you are, or have been, the parent of an adolescent, you’ve almost certainly experienced first-hand the phenomenon of circadian phase delay, even if you’ve never heard the term.
The child who was fast asleep by 8.30 pm, and charging into your room to bounce on your bed as soon as the sun rose, is now a creature of the night, suddenly coming to life at 9 pm, and impossible to rouse in the morning.
Circadian phase delay has its roots in changes in your teenager’s internal body clock, which occur not just in humans but in other mammalian species too.
All living beings have a circadian rhythm, a roughly 24 hour cycle of predictable fluctuations in their physiological processes which results in physical, behavioral – and in conscious beings, mental changes that follow a daily cycle.
Circadian rhythm is generated from inside us, by a complex networks of body clocks called ‘peripheral oscillators’, which both influence and are influenced by the ‘master oscillator’, a region in the hypothalamus, deep in the brain, called the suprachiasmatic nucleus.
Although internally generated, circadian rhythm is modulated by external cues, especially light.
This is important, because our circadian period is not exactly 24 hours. In fact, circadian means ‘about a day’. In adults, the circadian period, or internal day length, is roughly 24 hours and 10 minutes – slightly longer than the solar day. We rely on the daily rhythm of fluctuations in daylight to reset our internal clock each day, so that it synchs up with the solar day.
But not only does the circadian period become longer in adolescents, they also experience altered sensitivity to light cues at different times of day. Exposure to light in the evening delays their sleep phase more, while morning light is less effective at resetting their body clocks, than in adults.
In a nutshell, light exposure at night makes them more wakeful, and morning light fails to wake them up.
And therein lies the problem for 21st century teens. The advent of artificial lighting, and in the last decade, the ubiquitous use of light-emitting screens, creates the ‘perfect storm’: a confluence of biological and psychosocial factors that has resulted in an epidemic of chronic sleep deprivation in teenagers: only 15% of surveyed teenagers reported obtaining the recommended 8 1/2 hours of sleep on school nights.
Sleep deprivation doesn’t just result in the inertia and grumpiness that parents of teens dread facing, every school morning. It also compromises immunity, impairs academic performance, decreases impulse control (already a weakness during this life stage to the significant brain remodelling that takes place during adolescence), reduces insulin sensitivity and drives overeating of energy-dense food which may in turn fuel weight gain, and even ramps up pain perception. Long term sleep loss is associated with an increased risk of obesity, diabetes and heart disease.
So what can parents do to help their teenagers get more sleep? A study conducted by a team of Dutch researchers provides reinforcement for parents who have long suspected that teens and screens are not a good mix, especially at night.
The researchers, led by Dr Dirk Jan Stenvers from the department of Endocrinology and Metabolism of the Amsterdam UMC, recruited 25 Dutch adolescents aged 12–17 who reported 4 or more hours of screen use per day (frequent screen users), and 30 teens who used a screen for up to 1 hour per day (infrequent users).
They found that frequent screen users got to sleep on average 30 minutes later that infrequent users, woke up more often during the night, and suffered from more symptoms of sleep loss, such as tiredness and poor concentration.
But eliminating screen use, or wearing glasses that block exposure to the blue light emitted by screens, for just 1 week corrected the sleep disruption that heavy users of screens had been experiencing before the intervention. Participants who abstained from screen use got to sleep and woke up around 20 minutes earlier, and reported fewer symptoms of sleep loss.
As every parent knows, detaching a teen from their screen is rarely an easy task. Adolescents are generally not motivated by information about long-term health risks, but parents and teachers may be able to persuade them to power off well before bedtime by explaining the effects of screen use on their waistline, sports performance, or academic achievement.
And if all else fails, the deputy principal of my daughter’s high school has a helpful tip: since parents are generally the ones paying for their teen’s mobile phone, they can let their screen addict know that if the phone isn’t handed over to Mum or Dad at an agreed-upon hour, their plan will be cancelled.
Routers that provide parental control of logged-on devices are available… or just turn off the modem at dinner time and don’t switch it back on again.
After all, while teens’ circadian rhythms are particularly susceptible to disturbance by light at night, nocturnal screen use has destructive effects on adult sleep patterns too. Both adolescents and their parents will be better slept, and physically and mentally healthier, with reduced screen time.
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